This project is concerned with the objective classification and analysis of all electrocardiograms in the Coronary Drug Project. A standardized and centralized procedure is employed, with coding by trained technicians and with internal and external quality control. The measurements and classifications are entered into the central data file of the Baltimore Coordinating Center. The ECG Center participates in the analyses concerned with the objective use of the ECG to portray differences in randomly-assigned treatment groups, and with the natural history of coronary disease following myocardial infarction. The electrocardiographic characteristics and their changes are related to subsequent mortality and morbidity rates for infarct patients, crudely, and after adjustment for associated clinical prognostic factors.